A blue-green-emitting 3D supramolecular compound: synthesis, crystal structure and effect of solvents and temperature on the luminescent properties

Abstract

A blue-green-emitting three-dimensional supramolecular compound (C10O2N2H8)(C9O7H6) (1) was synthesised under hydrothermal conditions and structurally characterised by elemental analysis, IR spectrum, 1H NMR and single-crystal X-ray diffraction. The crystal belongs to triclinic system with P 1¯ space group. The crystal structure is stabilised by O–H…O, O–H…N hydrogen bonds and π–π interactions (π–π stacking distance is 3.282 Å). Compound 1 exhibits intense green luminescence in solid state at 298 K (λem = 546 nm). In addition, absorption and fluorescence characteristics of compound 1 have been investigated in different solvents (DMSO, CH3CN and CH3OH). The results show that compound 1 exhibits a large red shift in both absorption and emission spectra as solvent polarity increases (polarity: DMSO>CH3CN>CH3OH), indicating a change in dipole moment of compound 1 upon excitation. Although the emission spectra of compound 1 in CH3OH are close to it in dimethyl sulfoxide (DMSO), it is revealed that the luminescence behaviour of compound 1 depends not only on the polarity of environment but also on the hydrogen bonding properties of the solvent. Meanwhile, temperature strongly affects the emission spectra of compound 1. Emission peaks of compound 1 were blue shift at 77 K than those at 298 K in both solid state (ca. 142 nm) and solution (ca. 6–23 nm), which was due to the non-radiative transition decreases at low temperature. Moreover, the quantum yield and fluorescence lifetime of compound 1 were also measured, which increased with increasing polarity of solvent, lifetime in DMSO at 298 K (τ1 = 0.92 μs, τ2 = 8.71 μs) was the longest one in solvents (298 K: τ1 = 0.87–0.92 μs, τ2 = 7.50–8.71 μs; 77 K: τ1 = 0.72–0.90 μs, τ2 = 6.88–7.45 μs), which was also shorter than that in solid state (298 K: τ1 = 1.13 μs, τ2 = 7.50 μs; 77 K: τ1 = 0.97 μs, τ2 = 8.97 μs). This was probably because of the weak polarity environment of compound 1 in solid state.